Confirmation of the Geophysical Site Characterization Results by Tunnel Observations at Olkiluoto

A project for geological disposal of spent nuclear fuel deep into Finnish bedrock has been run now since 1988 in Eurajoki Olkiluoto, western Finland (Anttila et al. 1999, Enescu et al. 2004). The related research and development tasks are carried out by Posiva Ltd. A multiphase characterization with geological, hydrological, geophysical and hydrochemical methods have been run from ground surface and boreholes. One of the crucial tasks in the early investigation phases were recognition of avoidable volumes of bedrock, which are more fractured (faulted), sheared or altered rock sections in the bedrock mass of generally high quality. The initial design of underground spaces has based on interpretations of these ground and borehole studies. The excavation of access tunnel leading to future underground investigation facilities started in 2003. The tunnel profile is 6 m and its raise is 1/10. Tunnel will reach the level -420 m by 2010 then characterization will be continued at the -400…-500 m depth levels until 2020. Current tunnel length is 1030 m, and depth 100 m from ground level. The tunnel offers a new view for characterization and confirmation of the observations. The progress makes it possible to implement a prediction and confirmation cycle.